[0001] This invention relates generally to an imaging apparatus and method and, more particularly,
to a distributed ghost imaging apparatus and method for enabling long-range and/or
wide angled imaging of targets.
[0002] Modern tactical aircraft use a number of imaging aids to view external objects/scenes;
and visible, infrared and/or narrow-spectrum optical devices are used in various applications
to form an image of a scene. Real-time acquisition of high-resolution, wide field
of regard and high dynamic range images is essential for many military and civilian
surveillance applications. In order to achieve a wide field of regard, an imaging
device may be mounted on a gimbal, with a steering subsystem being provided to enable
the imaging device to be steered to cover a required field of view. In order to achieve
long range imaging, relatively large optical systems (i.e. long focal length and large
sensing aperture) are required; and in all cases, the imaging components, which tend
to be bulky and complex, are affixed to the host platform, which makes a significant
contribution to the overall size, weight and power associated with the host platform
subsystems.
[0003] It is an object of aspects of the present invention to address at least some of these
issues, and provide an imaging apparatus that can be readily configured to have a
wide field of regard and/or long range imaging capability, without significant detriment
to the size, weight and power contribution of the imaging system to the overall host
platform, whilst retaining an adequate resolution, such that real-time acquisition
of high resolution, wide field of regard and/or high dynamic range images can be achieved
in environments such as airborne platforms, where size, weight and power considerations
may be critical.
[0004] In accordance with an aspect of the present invention, there is provided imaging
apparatus for a host platform having an external surface, the apparatus comprising
a plurality of single pixel detectors distributed about said external surface, each
single pixel detector being configured to receive radiation reflected by an object
or region of interest and generate two-dimensional image data representative thereof,
the apparatus further comprising an image processing module for receiving said two-dimensional
image data from each of a plurality of single pixel detectors and reconstructing a
three-dimensional image of said object or region of interest using a ghost imaging
algorithm.
[0005] In an exemplary embodiment of the present invention, the apparatus may further comprise
a radiation source module including a radiation source. The radiation source module
may include a control device configured to adjustably direct an output of said radiation
source onto an object or region of interest. In an exemplary embodiment, the radiation
source module may comprise a target acquisition device for detecting an object or
region of interest and generating a signal configured to cause said control device
to direct said radiation source output to irradiate said detected object or region
of interest. The radiation source module may also comprise a tracking device for tracking
relative movement between the host platform and an object or region of interest and
generating a signal configured to cause said control device to adjust the direction
of said radiation source output such that irradiation thereby of said object or region
of interest is maintained.
[0006] In a first exemplary embodiment, the radiation source may comprise a structured light
source comprising a laser and a spatial light modulator through which light from said
laser passes before irradiating said object or region of interest. In this case, the
ghost imaging algorithm may be a computational ghost imaging algorithm. The spatial
light modulator may be configured to provide a time varying mask through which light
from said laser passes to irradiate said object or region of interest, said apparatus
further comprising a storage module for receiving data representative of a mask configuration
and associated time. The mask may be of spatially random configuration. In an exemplary
implementation, the spatial light modulator may comprise a digital micromirror device
including a programmable on/off duty cycle for effecting said time varying mask. The
radiation source may be provided on the host platform, at any suitable location. However,
in some exemplary embodiments, the radiation source may be provided at a location
geographically separated from said host platform. For example, the radiation source
may be provided on another platform, thereby decreasing the size, weight and power
overhead in relation to the host platform itself.
[0007] In a second exemplary embodiment, the radiation source may comprise a photon source
for generating a photon beam and an optical device located within said photon beam
configured to split photons from said beam into two or more entangled photons, and
may be configured to direct at least one of said entangled photons toward said object
or region of interest and another of said entangled photons to a detector, wherein
the apparatus may comprise a quantum correlation circuit configured to generate said
two-dimensional image data, and said ghost imaging algorithm may comprise a quantum
ghost imaging algorithm. In this case, the optical device may comprise a nonlinear
crystal.
[0008] At least some of said single pixel detectors may include a wireless data transceiver
configured to enable wireless data communication therebetween. For example, the wireless
data transceiver may comprise a short wavelength radio frequency transceiver. The
above-mentioned wireless data communication may comprise communication between said
single pixel detectors of one or more relevancy parameters indicative of one or more
similarities between respective states of said detectors. A state may comprise, for
example, pointing angle and/or field of regard of a respective single pixel detector.
If a relevancy parameter is determined to be met between two or more single pixel
detectors, the apparatus may be configured to cause the respective two-dimensional
image data output thereby to be integrated.
[0009] As stated above, the single pixel detectors are distributed about the external surface
or skin of the host platform. They may be parasitically mounted thereon but, in an
alternative exemplary embodiment, they may be integrally mounted within said external
surface.
[0010] The single pixel detectors may each include a local energy source for supplying electrical
energy thereto.
[0011] In accordance with another aspect of the present invention, there is provided an
imaging method for a host platform having an external surface, the method comprising
providing a plurality of single pixel detectors distributed about said external surface,
each single pixel detector being configured to receive radiation reflected by an object
or region of interest and generate two-dimensional image data representative thereof,
the method further comprising configuring an image processing module to receive said
two-dimensional image data from each of a plurality of single pixel detectors and
reconstruct a three-dimensional image of said object or region of interest using a
ghost imaging algorithm.
[0012] In accordance with yet another aspect of the present invention, there is provided
a radiation source module for apparatus as described above, comprising a radiation
source, a control device configured to adjustably direct an output of said radiation
source, and a target acquisition device for detecting an object or region of interest
and generating a control signal configured to cause said control device to direct
said output of said radiation source onto said object or region of interest. In this
case, the radiation source module may further include a tracking device for tracking
relative movement between the host platform and the object or region of interest and
generating a signal configured cause the control device to adjust the direction of
the radiation source output so as to maintain irradiation thereby of the object or
region of interest.
[0013] These and other aspects of the present invention will become apparent from the following
specific description in which embodiments of the present invention will now be described
by way of examples only and with reference to the accompanying drawings, in which:
Figure 1 is a schematic block diagram of imaging apparatus according to a first exemplary
embodiment of the present invention; and
Figure 2 is a schematic block diagram of imaging apparatus according to a second exemplary
embodiment of the present invention.
[0014] In general, Computational Ghost Imaging (CGI) involves the use of a structured light
source to illuminate an object or region of interest and a single pixel detector to
receive the reflections. The detector produces a two dimensional image of the object
or region of interest, where the resulting image is a function of the level and type
of illumination structure used by the illuminating system (i.e. the structured light
source).
[0015] Referring to Figure 1 of the drawings, a system according to an exemplary embodiment
of the present invention comprises a plurality of single pixel detectors 10, a structured
light source comprising a continuous wave (CW) or pulsed power laser (PPL) 12 and
a spatial light modulator (SLM) 14, and an image processing module 16.
[0016] Each single pixel detector 10 comprises a single photon detector configured to record
a measurement as an output voltage, representative of the quantity of light detected
by the photon detector. The detector further includes an A/D converter or microprocessor
for converting the above-mentioned measurement into a suitable digital representation
thereof, and a local energy source. The energy source may, for example, comprise an
electrical cell, such as a Lithium-ion cell or the like, but may alternatively comprise
a device that harvests energy from the local environment through, for example, solar
irradiation (e.g. using a solar photo-voltaic device), vibration (e.g. using a piezo
device), or thermal differences (e.g. using a thermionic device). However, other suitable
energy sources for a single pixel detector will be known to a person skilled in the
art and the present invention is in no way intended to be limited in this regard.
[0017] In a system according to an exemplary embodiment of the present invention, a plurality
of such single pixel detectors are utilised, which are applied parasitically to the
skin or external surface of a platform, or integrated therein so as to form a fundamental
part of its structure. Each single pixel detector may hereinafter be referred to as
a 'node', with each node including a short wavelength radio frequency transceiver
(e.g. 60 GHz) for wirelessly communicating its digital output to other nodes. The
respective outputs of the single pixel detectors are also communicably coupled to
the image processing module 16.
[0018] As stated above, the structured light source in this exemplary embodiment of the
present invention comprises a continuous wave (CW) or pulsed power laser (PPL) 12
and a spatial light modulator (SLM) 14. The SLM is configured to provide a time varying
(spatially random) 'mask' through which the laser light passes and thus gains spatial
information, which it ultimately conveys to the object or region of interest 18 and
then, by reflection, to one or more single photon detectors. Thus, the SLM 14 may,
for example, comprise a digital micromirror device (DMD) having multiple (thousands
or even millions of) individually controlled micromirrors built on top of an associated
CMOS memory cell. Each micromirror can be oriented in one of two directions: the 'on'
position or state allows light to pass through, and the 'off' position or state reflects
light incident thereon, thereby effectively blocking its passage through the device.
A controller loads each underlying memory cell with a '1' (on) or a '0' (off), and
a mirror reset pulse, when subsequently applied, causes each micromirror to be electrostatically
deflected about a hinge to the deflection angle corresponding to the state specified
by the value held in the associated memory cell. The on/off duty cycle of each micromirror
is fully programmable, such that the DMD can be readily used to provide the above-mentioned
time-varying 'mask'. However, other methods of providing a time-varying (spatially
random) 'mask' through which then laser light passes to gain the required spatial
information will be known to a person skilled in the art, and the present invention
is not necessarily intended to be limited in this regard. Furthermore, it will be
appreciated that the structured light source may be provided on the same platform
as the single pixel detectors (the 'host' platform) but may, alternatively, be located
on another platform that is geographically separated from the host platform, thereby
further decreasing the space, weight and power considerations in relation to the host
platform.
[0019] In use, laser light passes through the SLM 14, thus gaining spatial information which
is conveyed to the object or region of interest 18. Light is then reflected therefrom,
back to the single pixel detectors 10. Each single pixel detector system can only
output a single value corresponding to a time interval, which value is communicated
to the image processing module 16. However, if the illumination 'mask' being used
at a given time is known, then it is possible to create a multiplexed, two-dimensional
image from a larger number of these pixel values by correlating the known spatial
information from the captured signals. A number of processes for achieving this will
be known to a person skilled in the art, such as those that employ Hadamard 2D matrices
for example, and the present invention is not in any way intended to be limited in
this regard. Thus, irrespective of the process used, the image processing module 16
receives the measurements from the single pixel detectors and creates a multiplexed
two-dimensional image of the object or region of interest 18. Finally, the multiplexed
image can be fully reconstructed using any known computational ghost imaging algorithm,
such as an inverse Hadamard transform for example, but, once again, the present invention
is not intended to be in any way limited in this regard.
[0020] As stated above, each single pixel detector includes a short wavelength radio frequency
transceiver for enabling it to communicate its digital output to other nodes. Thus,
it is envisaged that at least some exemplary embodiments of the present invention
may include the facility whereby digital outputs from a plurality of single pixel
detectors (captured during the same time interval and, therefore, using the same 'mask')
can be correlated according to a predetermined one or more parameters (or 'relevancy')
and, subsequently, integrated before use thereof in the image reconstruction process.
[0021] All of the nodes will have a fixed, known pointing angle and field of regard relative
to each other and the host platform. The absolute pointing angle and field of regard
can additionally be determined by the host platform's inertial measurement unit. Thus,
for example, there may be circumstances whereby a plurality (or "cluster") of nodes
can be determined or known to have a similar pointing angle and field of regard with
respect to the object or region of interest. In this case, the digital signals output
by each of these nodes may be integrated, and the integrated signal then used in the
subsequent image reconstructions process. Such integration may be effected substantially
simultaneously (either in the image processing module or in a processing module of
one or more selected/predetermined nodes) and prior to the image reconstruction process,
and thus contributes to an element of decentralisation of the overall image processing
function. Thus, similar image signals can be combined to enhance the resolution of
the resultant image and/or boost the image signal above any noise, without significant
additional processing overhead. It will be appreciated by a person skilled in the
art that correlation on the basis of 'relevancy' is not necessarily limited to pointing
angle and field of regard, and it is envisaged that other correlation parameters may
be used/incorporated.
[0022] Overall, therefore, due to the utilisation of multiple, spatially distributed single
pixel detectors about a platform skin, a wide range of viewing angles can be achieved
and, therefore, a wide field of regard system achieved, subject only to the availability
of the structured illumination source to illuminate an object or region of interest.
Furthermore, the above-described coherent integration of detector pixel responses
allows for improvements in system sensitivity and, therefore, an increase in the imaging
or detection range of the system. Still further, both of these objects are achieved
by the use of single pixel, largely independent detectors, which are considered to
be highly advantageous in many applications, as they can be readily affixed to, or
incorporated into, any platform without significant space, weight or power issues
arising.
[0023] Quantum ghost imaging utilises a concept known as quantum entanglement which means
that multiple particles are linked together in a way such that the measurement of
one particle's quantum state determines the possible states of the other particles.
Measurements of physical properties such as position, momentum, spin, polarization,
etc. performed on entangled particles are found to be appropriately correlated. In
quantum ghost imaging, a succession of entangled photon pairs is created and, for
each pair, one of the photons is sent towards the object or region of interest and
the other is held back (and contained, for example, in a fibre-optic loop). When a
reflected photon is received from the object/region of interest, a correlation check
is performed with the photon(s) previously held back. If the correlation is positive,
then the contribution made by the reflected photon(s) to the ultimate formation of
the image is accepted. A negative correlation would result in the photon(s) contribution
being discounted, as they are not the photons used to illuminate the object/region
and, therefore, potentially represent noise that would otherwise pollute or corrupt
the image of the object/region.
[0024] Referring now to Figure 2 of the drawings, a system according to another exemplary
embodiment of the present invention comprises a plurality of single pixel detectors
100 and an image processing module 160. The system further comprises a light source
comprising a photon source, such as a laser 120 and an optical device such as a nonlinear
crystal 140 for causing a source photon to be split into two, entangled photons. Nonlinear
optic (NLO) crystals for generating entangled photons are known, and examples include
beta Barium Borate (BBO), Silver Gallium Sulfide (AgGaS
2) and Silver Gallium Selenide (AgGaSe
2). However, other examples of nonlinear crystals will be known to a person skilled
in the art, and the present invention is not in any way intended to be limited in
this regard. It will be further appreciated by a person skilled in the art that the
source photon can be split into more than two entangled photons, as required. In this
case, a photon source and optical device arrangement will be provided in respect of
each single pixel camera, and co-located therewith, so as to retain the required spatial
information (on the basis that the source location in relation to the object or region
of interest is thus known).
[0025] In use, each photon source 120 fires photon pulses into the non linear crystal 140,
which causes each source photon to be split into two (or more) entangled photons.
At least one of the entangled photons is directed (by the crystal or other optical
elements, not shown) into a fibre optic loop or other storage device 190 in the image
processing module 160 and the remaining entangled photon(s) is/are directed toward
the object or region of interest 180. The photons reaching the object or region of
interest 180 are reflected back to the single pixel detectors 10 which create respective
digital signals representative of the photons incident thereon, retaining the respective
physical properties of the received photon(s). The image processing module 160 receives
the digital outputs from the single pixel cameras and includes a quantum correlation
circuit (QC) including a quantum detector configured to compare each photon received
from the single pixel camera against photons contained within the fibre-optic loop
to determine if it is a photon which originated from the source. If it is determined
not to have originated from the source, the photon is discarded as noise. If the photon
is determined to have originated from the source, it is used to generate respective
two-dimensional image data. The image processing module 160 then creates a multiplexed
two-dimensional image of the object or region of interest 180, as before. Finally,
the multiplexed image can be fully reconstructed using any known ghost imaging algorithm.
[0026] In an alternative exemplary embodiment, each single pixel detector module could include
its own quantum correlation circuit that has access to the fibre-optic loop or other
storage device 190. Thus, in this case, upon receipt of a photon, the respective QC
circuit would transmit a request to the storage device 190 for data representative
of the original entangled photons and use the returned data to perform the require
quantum correlation in respect of the received photon. In this case, the data returned
to the QC circuit in response to a request therefrom might be in a converted form,
wherein the central processing module includes means for converting the stored photons
from an entangled state into another state (e.g. radio frequency) for transmission
to the individual QC circuit(s).
[0027] In both exemplary embodiments, and others, the light source may be part of a radiation
source module including some means for ensuring that the radiation is directed and
maintained on the object or region of interest. In an exemplary embodiment, the module
may, for example, include a target acquisition device for scanning the environment
within the field of regard of the imaging apparatus and identifying an object to be
imaged. Alternatively, of course, the object or region of interest can be manually
defined and light source electronically driven and guided accordingly, but in either
case, the module may further comprise a motion tracking device for tracking relative
movement between the host platform and the object or region of interest and generating
a signal configured to operate a guide mechanism for guiding the light source such
that the radiation emitted thereby consistently and accurately irradiates the object
or region of interest.
[0028] It will be apparent to a person skilled in the art, from the foregoing description,
that modifications and variations can be made to the described embodiments without
departing from the scope of the invention as defined in the appended claims.
1. Imaging apparatus for a host platform having an external surface, the apparatus comprising
a plurality of single pixel detectors distributed about said external surface, each
single pixel detector being configured to receive radiation reflected by an object
or region of interest and generate two-dimensional image data representative thereof,
the apparatus further comprising an image processing module for receiving said two-dimensional
image data from each of a plurality of single pixel detectors and reconstructing a
three-dimensional image of said object or region of interest using a ghost imaging
algorithm.
2. Apparatus according to claim 1, further comprising a radiation source module including
a radiation source.
3. Apparatus according to claim 2, wherein the radiation source module includes a control
device configured to adjustably direct an output of said radiation source onto an
object or region of interest.
4. Apparatus according to claim 2 or claim 3, wherein the radiation source module comprises
a target acquisition device for detecting an object or region of interest and generating
a signal configured to cause said control device to direct said radiation source output
to irradiate said detected object or region of interest.
5. Apparatus according to any of claims 2 to 4, wherein the radiation source module comprises
a tracking device for tracking relative movement between the host platform and an
object or region of interest and generating a signal configured to cause said control
device to adjust the direction of said radiation source output such that irradiation
thereby of said object or region of interest is maintained.
6. Apparatus according to any of claims 2 to 5, wherein the radiation source comprises
a structured light source comprising a laser and a spatial light modulator through
which light from said laser passes before irradiating said object or region of interest.
7. Apparatus according to claim 6, wherein the spatial light modulator is configured
to provide a time varying mask through which light from said laser passes to irradiate
said object or region of interest, said apparatus further comprising a storage module
for receiving data representative of a mask configuration and associated time.
8. Apparatus according to any of claims 2 to 5, wherein the radiation source comprises
a photon source for generating a photon beam and an optical device located within
said photon beam configured to split photons from said beam into two or more entangled
photons, and may be configured to direct at least one of said entangled photons toward
said object or region of interest and another of said entangled photons to a detector,
wherein the apparatus may comprise a quantum correlation circuit configured to generate
said two-dimensional image data, and said ghost imaging algorithm comprises a quantum
ghost imaging algorithm.
9. Apparatus according to claim 8, wherein the optical device comprises a nonlinear crystal.
10. Apparatus according to any of the preceding claims, wherein at least some of said
single pixel detectors include a wireless data transceiver configured to enable wireless
data communication therebetween.
11. Apparatus according to any of the preceding claims, wherein said single pixel detectors
are parasitically mounted on said host platform, or integrally mounted within said
external surface thereof.
12. Apparatus according to any of the preceding claims, wherein the single pixel detectors
each include a local energy source for supplying electrical energy thereto.
13. An imaging method for a host platform having an external surface, the method comprising
providing a plurality of single pixel detectors distributed about said external surface,
each single pixel detector being configured to receive radiation reflected by an object
or region of interest and generate two-dimensional image data representative thereof,
the method further comprising configuring an image processing module to receive said
two-dimensional image data from each of a plurality of single pixel detectors and
reconstruct a three-dimensional image of said object or region of interest using a
ghost imaging algorithm.
14. A radiation source module for apparatus according to any of claims 2 to 12, comprising
a radiation source, a control device configured to adjustably direct an output of
said radiation source, and a target acquisition device for detecting an object or
region of interest and generating a control signal configured to cause said control
device to direct said output of said radiation source onto said object or region of
interest.
15. A module according to claim 14, including a tracking device for tracking relative
movement between the host platform and the object or region of interest and generating
a signal configured cause the control device to adjust the direction of the radiation
source output so as to maintain irradiation thereby of the object or region of interest.